I just saw a picture of a BMW or Mercedes engine with the 8 coils above the cover. If there were a good way to ensure that water could not get around the boot over the sparkplug hole, I would say go for it. The boot should keep most all dirt out.

I washed a friends 854T5 engine a while back, the car lived on a dirt road!! After washing the engine bay down with a garden hose and a finger to provide some pressure (with the engine running), I deceided to drive around the block to help things dry out. Well, I almost made it :) First, 1 cyl misfired, then another, the CEL came on, then it just died. When I pulled the cover off, it was dry. But, when I pulled the plug wire out, there was an inch or two of water in every hole! I used a rag to soak up the water - very hot!!! - and then waited 2 hours before starting it up again. I also found out that the distributer cap had a large crack in it. New plugs, wires, rotor and cap are on my workbench waiting for the T5 to visit again.

Klaus
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The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)